Thermionic tube



Feb. 19,Y 1935.

P. F SCOFIELD THERMIONIC TUBE Filed July 18, 1932 0 Q 0 A M 2 a INI/ENTOR7 P /L/P E SCOF/ELD.

ATTORNEY Patented Feb. 19, 1935 PATENT OFFICE;

s ,s THEnMioNIc TUBEl v Philip F. Scofleld,Palo Alto, Calif., assigner to .Heintz & Kaufman, Ltd., San Francisco, Calif., ,acorporation of Nevada Application July "1s, 19.32, seria1No.6zs,116 11 Claims. (Cl. Z50-#4275) My invention relates to thermionic tubes, and particularly to tubes for delivering. relatively large Vpower voutput at low-voltage. Y

`Amongfthe objectsrof my invention are: To 5 provide atube having annextremely lowoutput o impedance; .to I provide` a Vthermionic l tube capable of handling large"amountsV of currenty atlow voltage; to provide a thermionic tube which may be voperated directlyfrom direct current supplies at commercial voltages, without the necessity of rotary converters, or equivalent auxiliary equipment; to provide a thermionic tube particularly adapted for ship-board use; to `provide, a tube wherein the electrodes'are permanently and rigidl5 ly heldin their properrelative positions; to provide a tube structure'wherein the elements are v supported frcmboth ends without introducing temperature stresses; Vto provide a tube requiring the use of relatively small vauxiliaryfpower for heating the cathode; and to provide a tube which Vis freefrom the microphonicnoises due relative vibration of theelements. j,

Other-,objects of my invention will be apparent or will be specifically pointed out in the-description forming a -partofthis specicatiombut I do notlimit myself to' the embodiment of myrinvention herein described, Vas various forms may be adopted within the scope of theclaims.v

Y AReferring to the drawing: Y I

Figurel is an vaxialsectional view through a tube embodying this invention; A

Figurez is a transverse sectional view of the tube shown in the firstY figure, the lplane of projectionbeing on the liner2-2 of Figure 1.

Figure. 3 is an elevation showing the cathode of the tube, together with its insulating supports.

In general terms,` the tube of my invention comprises the usual envelope, within which is mountedA an insulating refractory barrier, to one surface of which is applied the surface of a control electrode ofthe plate type. The Opposed surface of the barrier carries a thermionic lcathode in the form of a grill, i. e.the cathode canhave any form, helical, grid, orv reticulated, which exposes portions of the barrier between its elementary parts.r VSpaced from the cathode is an anode, which is preferably mounted onthe barrier with its points of 'contact therewith relatively remotel to the 1 ,endofa barrier tube 9 which is Vformed ofV reextremely large emitting surface,` and spaced more closely with respect to the anode than is feasible with separately supported structures.v The cath-V ode may be self-heated, but heat is preferably supplied from-a separate unit mounted within 5 the tubular barrier, and the anode, heating ele- Vment, and controlelectrode are formed of materials such as tantalum, or 'chromium or its alloys, which areY poor electron emitters, requiring tofbe raised to an extremely high temperature before 1Q material thermionic emissionoccurs. The cathode, on the contrary, has-a surface ofhigh electron emissivity, and -is maintained at emissive temperature -not only by thenheater, butalso .by heat radiatedinward from the anode.V

A preferred embodiment of my invention comprises a tubular envelope 1,V having ure-entrant stems 2 and 3 sealed into eachend.` Surrounding the stem 2is a clamp 5; to which arewelded support wiresgcarrying a second clamp 7.. 20

:The clamp 'l surrounds and supports 4the open fractoryjinsulating material having a relatively rhighdielecinic constant. Synthetic Ycorundum,

such as is `sold under the trade-name alundum, :g5 is at present thelpreferredV material for forming this barrier, owing to its high dielectric constant and to thev fact that lit retains lhigh dielectric strength and resistivityv evenr under relatively high temperatures. 1 Magnesium oxide, lava or other; 3 0 refractory insulating materials maybe used in place of the corundum'if care is taken to operate them at temperatures below which they become conductive. Y Y i Y Within the barrier tube 9- is fitted a cylindrical 55 electrode 10, which is of suchdiameter as to engage the inner wall'of the tube closely, making frictional contact therewith. A vlead 11 makes contact with the electrode 10 and is sealed out 40 through the 4stem 2.'.v Y v y Closely surrounding-the outer surface ofthe tube 9, opposite the control electrode 10, is a thermionic Vcathode 12. The vcathode isvpreferablyv made ofA nickel, and is coated` with alkali earth 45 oxide or other materials having high frelectron emissivityat low temperatures. The cathode is held frictionally on Vthe tube 9, andis in the form of a grill or grid, so that portions of the surface of thetube are exposed between the various ele- .ments of the cathode.` As shown, the cathode comprises a pair of rings joined by parallel bars,

but 'it may be vhelical or reticulated in form if desired. .Y o

The'cathodemay be self-heated, by connecting` 55 a lead 14 to one of the end rings, and a similar lead to the other, the bars being in parallel. I prefer', however, to provide a separate heating element 15 within the tube 9, which is supplied by leads 16, passing through the'stem 2, and to seal the lead 14. out through the opposite stem 3. In this case the insulating tube 9, control electrode 10, and cathode 12, are all raised to a relatively high temperature, but only the cathode will emit electrons, owing to the low thermionic emissivity of the electrode 10. With this construction it is preferred that the insulating tube 9 be provided with a dome-shaped closure 17, formed integrally therewith, overpthe end opposite the supporting clamp 7, since this assists in retaining the heat emitted by the element 15'.

It will be seen that the tube V9v forms an insulating barrier'between theV control electrode 10 and the grid 12. Because of the high dielectric constant `ot' this barrier, the effect of the electrode 10 upon electrons emitted from the cathode is'the same as it wouldbe wereV the electrodes much more closely spaced in vacuo wtihout the intervening barrier. v j I y Surrounding the barrier and the cathode is an'anode 20, also of cylindrical form,'and lhaving inturned flanges 21 on reach end which contact the barrier 'and determine definitely the spacing between the cathode andthe anode.Y The anode is materially" longer than the cathode, so that the leakage path alongthe barrier is much greater than vthe path of the electrons Abetween the two electrodes in free space. One of the iianges 21 is provided with' aY notch 22V to permit the passage of the lead 1li.` A lead-24, welded or otherwise securedto the anode, positions it longitudinally of the tube and is sealedthrough the stem 3.

The tube thus describedoperate's aseither deftector,"oscillatfor, or amplifier, in much the'same manner asthe ordinary three Velectrode tube hav'- ingV a grid interposed between the Vanode land cathode. Its impedance, however, is very much less than the grid type of tube; owing to the lfree path between the cathode Vand anodejand especially due to the fact that the rigid construct'- tion permits extremely Vclose spacing between the tube elements. Control is exercised by the iields of theelectrode 10, acting throughjthefopenings inthe grill-like cathode. Changes Vin potential of the control electrode change the number'of lines of force from the anode which terminate on the cathode. This varies the potential gradient at the cathode surface and'hence the space current.

The construction of the tube iseXtremely rigid, since the electrode assembly is Vsupported at both ends. Relative vibration between the electrodes is practically impossible, 'owing tothe fact that all of themY are frictionally in contact with the barrier tube. The construction, however, permits'slight longitudinal movement between lthe electrodes, and prevents the setting up' of longitudinal 'tempVerature` stresses.

Another factor which tends to make the imwith direct current of commercial voltages.

Since the heater 15 does not form a part of the tube circuit, it may be made tooperate on voltages of the same order as the -plate voltage, being` 'connected directly across the same line.

The tube is relativelyeconomical in its conv suinption of heater current, since the power which is ordinarily wasted in the plate circuit assists in heating the cathode. of chromium alloys for the plate permits it to be operated-.at the same temperature'asthecathode without failure of tube function ldue. toanode emission. Emission from the vcontrol electrode The use of tantalum or 1o Y .would do little harm in the absence of the heat- Yf j ingelement 15, but since it is desirable that a p single` source of power be used for both heaterl and platecircuitsfit is much to `be preferred that i both the element 10 and the heater 15 be made of non-emitting materials.

I claim: j

1. A thermionic tube comprising an insulating barrier, a control electrode having an extended surface in contact with one side of said barrier, a thermionic cathode comprising a conductive grillA in contact with the opposite surfaceY of said -ba'r rier,` and an anode spaced from said cathode` and supported by `said barrier, thespacingbetween saidcathode and anode along said barriergbeingl relatively great as comparedto the el tran f 2. A thermionic Vtube` Ycomprising a cylindrical insulating barrier, a `cylindrical control electrode` in Vcontaci-,with one side of said barrier, athermionic` cathode. comprising a cylindrical'fgrill in contactwith` the other side of said barrier, andav y cylindrical anode spacedfrom saidc'athode 'to` cylindrical anode spacedffrom'said 'cathode "tol provide-a free electronfpath' therebetween,V saidr anode being of greater length than said-cathode and'having supporting flanges thereon Vcontacting with said barrier. f Y

4.Y Athermionic tube comprising a cylindrical 'insulating barrier, a cylindrical controlelectrodj mounted :onjthe inner surface V`cf said' barrier, a

thermionic'cathode comprising a cylindrical grill Y.

mounted on the outer surface of said barrier, and

supported by said barrier.

a cylindrical anode-surrounding saidV cathode and 5.V A thermionic 'tube'comprising a cylindrical 'f insulating barrier, a cylindrical control electrode mounted on the 'inner Surface of said barrier, a thermionic'cathode comprising a cylindrical grill mounted onvthe outer surface of saidfvbarrierf'a vcylindrical anode surrounding said cathode, 'and flanges projecting inward from said anode and contacting said barrier to support said anodeL'v 6. A thermionic tube comprising a cylindrical "insulating, barrier, a cylindrical control electrode `mounted OIrthe inner'surfac'e of said 'barriena thei'mioniccathode comprising a cylindrical grill Y vmounted on the outer surface of said barrier',"` av cylindrical anode surrounding said cathodefand means within said barrier for raising said cathode y to electron-emitting temperature.

7. A thermionick tube comprising,A a,cylindricalYY 'Y =70 l insulating barrier, a cylindrical control electrode mounted` on the inner surface of saidlbarrier, a

i-hermionic cathode comprising a cylindrical grill ,mounted onthe outer surface of saidbarrier, a

cylindrical anode surrounding said cathode, and a radient heating element disposed withinthe barrier for raising said barrier and cathode to the electron-emitting temperature of the cathode.

8. A thermionic tube comprising an evacuated envelope, a rigid insulating cylinder supported Within the envelope, al control electrode mounted Within the cylinder and supported thereby, a thermionic cathode comprising a cylindrical grill closely surrounding said cylinder and supported thereby, and a cylindrical anode surrounding said cathode and spaced therefrom.

9. A tliermionic tube comprising an evacuated envelope, arigid insulating rcylinder supported within the envelope, a control electrode mounted Within the cylinder and supported thereby, a therniionic cathode comprising a cylindrical grill closely surrounding said cylinder and supported thereby, and inturned flanges on the ends of said anode contacting said cylinder to determine the relative positions of said cathode and anode.

10. A thermionic vacuum tube comprising an insulating tube, a cylindrical control electrode of relatively low electron emissivity supported in contact with the interior ysurface of said tube, a

cylindrical'cathode comprising a grill of relatively high electron emissim'ty supported by said tube in contact With the exterior surface thereof opposite to said control electrode, and an anodeV fof relatively low electron lemissivity surrounding said cathode.

11. A thermionic tube comprising a cylindrical envelope having a stem sealed in each end thereof,

f an insulating tube supportedv on one of said stems,

a cylindrical control electrode frictionallyVV engaging the interior surface of said tube, a thermionic vcathode surrounding Vsaid tube, a cylindrical anode surrounding said -cathode and anode and spaced therefrom, inturned flanges on the ends of said anode contacting said tube and'supporting said anode, and a supporting lead sealed through the other stem and connected to said 

